Method and system for three-dimensional data acquisition

ABSTRACT

A method for three-dimensional data acquisition, adapted to acquire three-dimensional data of an object, includes the following steps. A laser light is projected onto a plurality of regions on the surface of the object so as to form a plurality of features within each of the regions. For each of the regions, the object and the features are captured from a first direction and a second direction simultaneously so as to generate a first object image corresponding to the first direction and a second object image corresponding to the second direction. For each of the regions, the first object image and the second object image are processed so as to obtain the two-dimensional coordinates of the features therein. The three-dimensional data of the object is obtained according to the two-dimensional data of the features in the first object image and the second object image corresponding to each of the regions.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan applicationserial no. 102137943, filed on Oct. 21, 2013. The entirety of theabove-mentioned patent application is hereby incorporated by referenceherein and made a part of this specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a method and a system fordata acquisition, in particular, to a method and a system forthree-dimensional data acquisition.

2. Description of Related Art

In terms of three-dimensional (3D) surface-geometry measurement in thefield of computer graphics, the applications include industrial design,reverse engineering, medical image processing, criminal identification,digital documentation of culture artifacts, archaeological artifacts,which may extensively require 3D imaging and data analysis. Moreover,the manufacturing revolution triggered by 3D scanners and 3D printers inrecent years reveal the importance of 3D geometry data acquisition.

Conventional 3D laser scanners mostly include transmission componentssuch as rotating mechanisms or moving mechanisms for carrying an objectand are able to acquire 3D data of the object in a wider range bychanging measuring positions. Such design may require highermanufacturing costs and additional calibration processes. On the otherhand, the measuring approach without the usage of transmissioncomponents such as projecting a structured light may only provide acertain resolution, but not 3D data acquisition with a higher resolutionfor a local or particular region. Hence, to quickly and preciselyacquire the 3D data of an object through the use of adjustableresolutions and components with low costs is one of the tasks to besolved.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method and a systemfor three-dimensional (3D) data acquisition, which quickly and preciselyacquire the 3D data of an object through the use of adjustableresolution.

The present invention is directed to a 3D data acquisition method. Themethod includes the following steps: projecting a laser light onto aplurality of regions on a surface of the object so as to form aplurality of features within each of the regions; for each of theregions, capturing the object and the features from a first directionand a second direction simultaneously so as to generate a first objectimage corresponding to the first direction and the second object imagecorresponding to the second direction; for each of the regions,processing the first object image and the second object image so as toobtain two-dimensional (2D) coordinates of the features in the firstobject image and the second object image; and obtaining the 3D data ofthe object according to the 2D data of the features in the first objectimage and the second object image corresponding to each of the regions.

According to an embodiment of the present invention, for each of theregions, before the step of processing the first object image and thesecond object image so as to obtain the 2D coordinates of the featuresin the first object image and the second object image, the methodfurther includes the following steps: capturing a calibration objectfrom the first direction and the second direction so as to generate afirst calibration image corresponding to the first direction and asecond calibration image corresponding to the second direction; andprocessing the first calibration image and the second calibration imageso as to generate a first intrinsic parameter, a first extrinsicparameter, and a first lens distortion parameter corresponding to thefirst calibration image as well as a second intrinsic parameter, asecond extrinsic parameter, and a second lens distortion parametercorresponding to the second calibration image, wherein the firstextrinsic parameter and the second extrinsic parameter correspond to asame coordinate system.

According to an embodiment of the present invention, for each of theregions, the steps of processing the first object image and the secondobject image so as to obtain the 2D coordinates of the features in thefirst object image and the second object image includes: performing anundistortion calculation on the first object image and the second objectimage according to the first lens distortion parameter and the secondlens distortion parameter so as to generate a first corrected objectimage and a second corrected object image; obtaining 2D coordinates of aplurality of first features and a plurality of second features, whereinthe first features are the features in the first corrected object imageand the second features are the features in the second corrected objectimage; and obtaining a 2D coordinate of a correspondence of each of thefirst features from the second corrected object image according to eachof the first features and a first epipolar line corresponding to each ofthe first features as well as obtaining a 2D coordinate of acorrespondence of each of the second features from the first correctedobject image according to each of the second features and a secondepipolar line corresponding to each of the second features.

According to an embodiment of the present invention, the step ofobtaining the 3D data of the object according to the features in thefirst object image and the second object image corresponding to each ofthe regions includes: obtaining the 3D data of the object according to afirst projection matrix, a second projection matrix, the 2D coordinatesof the first features corresponding to each of the regions, the 2Dcoordinates of the correspondences of the first features correspondingto each of the regions, the 2D coordinates of the second featurescorresponding to each of the regions, and the 2D coordinates of thecorrespondences of the second features corresponding to each of theregions, wherein the first projection matrix is a matrix formed by thefirst intrinsic parameter and the first extrinsic parameter, and whereinthe second projection matrix is a matrix formed by the second intrinsicparameter and the second extrinsic parameter.

According to an embodiment of the present invention, after the step ofobtaining the 3D data of the object according to the features in thefirst object image and the second object image corresponding to each ofthe regions, the method further includes the following step: generatinga plurality of triangular meshes according to the 3D data of the objectand accordingly constructing a 3D model of the object.

The present invention is directed to a 3D data acquisition systemincluding a light projecting device, a first image capturing device, asecond image capturing device, and an image processing device. The lightprojecting device is adapted to project a laser light onto a pluralityof regions on a surface of the object so as to form a plurality offeatures within each of the regions. For each of the regions, the firstimage capturing device and the second image capturing device are adaptedto capture the object and the features from a first direction and asecond direction simultaneously so as to generate a first object imagecorresponding to the first direction and the second object imagecorresponding to the second direction. For each of the regions, theimage processing device is adapted to process the first object image andthe second object image so as to obtain 2D coordinates of the featuresin the first object image and the second object image, and obtaining the3D data of the object according to the 2D data of the features in thefirst object image and the second object image corresponding to each ofthe regions.

According to an embodiment of the present invention, for each of theregions, the first image capturing device and the second image capturingdevice further capture a calibration object from the first direction andthe second direction so as to generate a first calibration imagecorresponding to the first direction and a second calibration imagecorresponding to the second direction. For each of the regions, theimage processing device processes the first calibration image and thesecond calibration image so as to generate a first intrinsic parameter,a first extrinsic parameter, and a first lens distortion parametercorresponding to the first calibration image as well as a secondintrinsic parameter, a second extrinsic parameter, and a second lensdistortion parameter corresponding to the second calibration image,where the first extrinsic parameter and the second extrinsic parametercorrespond to a same coordinate system.

According to an embodiment of the present invention, for each of theregions, the image processing device performs an undistortioncalculation on the first object image and the second object image so asto generate a first corrected object image and a second corrected objectimage. For each of the regions, the image processing device obtains 2Dcoordinates of a plurality of first features and a plurality of secondfeatures, wherein the first features are the features in the firstcorrected object image and the second features are the features in thesecond corrected object image. For each of the regions, the imageprocessing device obtains a 2D coordinate of a correspondence of each ofthe first features from the second corrected object image according toeach of the first feature and a first epipolar line corresponding toeach of the first features as well as a 2D coordinate of acorrespondence of each of the second features from the first correctedobject image according to each of the second features and a secondepipolar line corresponding to each of the second features.

According to an embodiment of the present invention, the imageprocessing device obtains the 3D data of the object according to a firstprojection matrix, a second projection matrix, the 2D coordinates of thefirst features corresponding to each of the regions, the 2D coordinatesof the correspondences of the first features corresponding to each ofthe regions, the 2D coordinates of the second features corresponding toeach of the regions, and the 2D coordinates of the correspondences ofthe second features corresponding to each of the regions, wherein thefirst projection matrix is a matrix formed by the first intrinsicparameter and the first extrinsic parameter, and wherein the secondprojection matrix is a matrix formed by the second intrinsic parameterand the second extrinsic parameter.

According to an embodiment of the present invention, the imageprocessing device further generates a plurality of triangular meshesaccording to the 3D data of the object and accordingly constructs a 3Dmodel of the object.

To sum up, the method and the system for 3D data acquisition provided inthe present invention may generate a plurality of features on an objectthrough projecting a laser light onto a plurality of regions of theobject by the light projecting device. A plurality of image sets of theobject and the features may be captured by two image capturing devicesfrom different directions, and the 2D coordinates of the features in theimage sets may be calculated by an image processing device so as toobtain the 3D data of the object. Moreover, the moving rates, rotatingposes, and the number of repeating scans of the light projecting devicemay be adjusted according to the contour complexity of the object so asto adjust the scan resolutions in both the horizontal direction and thevertical direction. Such method and system of 3D data acquisition maynot only adjust the resolution with low costs, but may also processimages in real time so as to provide a higher applicability in practicaluse.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 illustrates a 3D data acquisition system according to anembodiment of the present invention.

FIG. 2 illustrates a flowchart of a 3D data acquisition method accordingto an embodiment of the present invention.

FIG. 3 illustrates a flowchart of an image calibration method accordingto an embodiment of the present invention.

FIG. 4 illustrates a flowchart of a 3D data acquisition method accordingto an embodiment of the present invention.

FIG. 5A and FIG. 5B illustrate partially magnified images of a firstcorrected object image and a second corrected object image capturedsimultaneously.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the present embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers are used in thedrawings and the description to refer to the same or like parts. Inaddition, the specifications and the like shown in the drawing figuresare intended to be illustrative, and not restrictive. Therefore,specific structural and functional detail disclosed herein are not to beinterpreted as limiting, but merely as a representative basis forteaching one skilled in the art to variously employ the presentinvention.

FIG. 1 illustrates a three-dimensional (3D) data acquisition systemaccording to an embodiment of the present invention. It should, however,be noted that this is merely an illustrative example and the presentinvention is not limited in this regard. All components of the 3D dataacquisition system and their configurations are first introduced inFIG. 1. The detailed functionalities of the components are disclosedalong with FIG. 2.

Referring to FIG. 1, a 3D data acquisition system 100 includes a lightprojecting device 110, a first image capturing device 120A, a secondimage capturing device 102B, and an image processing device 130. In thepresent embodiment, the 3D data acquisition system 100 may performscanning on an object A so as to acquire the three dimensional data ofthe object A.

In the present embodiment, the light projecting device 110 is a linearlight source and adapted to project a laser light onto the object A.When the light projecting device 110 projects, for example, a red laserlight onto the object A, a linear or curved red slit region may beformed on the surface of the object A. Moreover, the light projectingdevice 110 may be moved arbitrarily by a user or a moving mechanism sothat the laser light may be projected onto any spot on the surface ofthe object A.

In the present embodiment, both the first image capturing device 120Aand the second image projecting device 120B may be cameras with chargecoupled devices (CCD) and have fixed focal lengths. However, the presentinvention is not limited herein. In the present embodiment, the firstimage capturing device 120A and the second image capturing device 120Bmay be locked on a stand board so that the relative positions betweenthe two devices are fixed. In other words, the angle between the viewingdirections of the first image capturing device 120A and the second imagecapturing device 120B are fixed. The viewing directions of the firstimage capturing device 120A and the second image capturing device 120Bare referred to as “a first direction” and “a second direction”respectively. The first image capturing device 120A and the second imagecapturing device 120B are configured to continuously and simultaneouslycapture images of the object A.

In the present embodiment, the image processing device 130 may be apersonal computer, a notebook computer, a smart phone, a tabularcomputer, and yet the present invention is not limited thereto. Theimage processing device 130 includes a memory and a processor. Thememory is adapted to store the images captured by the first imagecapturing device 120A and the second image capturing device 120B, whilethe processor is configured to process the images stored in the memory.Furthermore, the image processing device 130 may obtain the imagescaptured by the first image capturing device 120A and the second imagecapturing device 120B via wired transmission or wireless transmission.

FIG. 2 illustrates a flowchart of a 3D data acquisition method accordingto an embodiment of the present invention. The 3D data acquisitionmethod in FIG. 2 may be implemented by the components of the 3D dataacquisition system 100 in FIG. 1.

Referring to both FIG. 1 and FIG. 2, the light projecting device 110projects a laser light onto a plurality of regions on the surface of theobject A so as to generate a plurality of features within each of theregions (Step S201). In the present embodiment, the object A may be aportrait sculpture with an irregular contour on the surface. Suchregions are the aforementioned linear or curved slit regions formed onthe surface of the object A. As illustrated in FIG. 1, when the lightprojecting device 110 project a red laser light onto the object A, a redregion M may be formed on the surface of the object A. Since the objectA has an irregular contours on the surface, a plurality of bright points(not shown) or a plurality of curved bright bands may be formed withinthe region M. Such bright points or bright bands may be referred to asthe aforementioned features. Since the light projecting device 110 maybe moved arbitrarily by the user or the moving mechanism, when the lightprojecting device 110 projects the laser light onto another region onthe surface of the object A, a plurality of features may also be formedon the another region. To acquire the complete 3D data of the object A,the light projecting device 110 may project the laser light onto all ofthe regions on the surface of the object A so as to form a plurality ofcurves and features. However, only the region M may be illustrated inthe present embodiment for simplicity.

Next, for each of the regions, the first image capturing device 120A andthe second image capturing device 120B may simultaneously capture theobject A and the features from the first direction and the seconddirection so as to generate a first object image and a second objectimage respectively (Step S203). For example, when the region M is formedon the surface of the object A, the first image capturing device 120Aand the second image capturing device 120B may capture the object A, theregion M and the features within the region M simultaneously from thefirst direction and the second direction. The first image capturingdevice 120A and the second image capturing device 120B may generate animage set including the first object image and the second object image.When another region is formed on the surface of the object A, the firstimage capturing device 120A and the second image capturing device 120Bmay also capture the object A, the another region, and the features onthe another region from the first direction and the second directionsimultaneously and generate another image set of the first object imageand the second object image. Analogously, when the light projectingdevice 110 projects the laser light onto the other regions on thesurface of the object A in Step S201, the first image capturing device120A and the second image capturing device 120B may generate a pluralityimage sets of the first object image and the second object image.

Next, for each of the regions, the image processing device 130 mayprocess the first object image and the second object image so as toobtain the two-dimensional (2D) coordinates of the features in the firstobject image and the second object image (Step S205). That is, after theimage processing device 130 obtains the image set of the first objectimage and the second object image for each of the regions via wiredtransmission or wireless transmission, it may calibrate the imagedistortion in the first object image and the second object image of eachof the image sets caused by the first image capturing device 120A andthe second image capturing device 120B. During the calibration process,the first image capturing device 120A and the second image capturingdevice 120B may generate a plurality of calibration parameters. Sincethe features are the bright points formed on the contour surface of theobject A, the image processing device 130 may detect the features in thefirst object image and the second object image of each of the image setsbased on, for example, brightness values so as to obtain the 2Dcoordinates of all the features.

Next, the image processing device 130 may obtain the 3D data of theobject A according to the 2D coordinates of each of the features in thefirst object image and the second object image corresponding to each ofthe regions (Step S207). In the present embodiment, the image processingdevice 130 may obtain the 3D data of the object A according to thecalibration parameters generated by the first image capturing device120A and the second image capturing device 120B as well as the 2Dcoordinates of each of the features in the first object image and thesecond object image corresponding to each of the regions by singularvalue decomposition (SVD).

The method for calculating the calibration parameters and the 2Dcoordinates in Step S205 as well as the method for calculating the 3Ddata of the object A by using the 2D coordinates of all the features inStep S207 will be discussed in the following descriptions.

FIG. 3 illustrates a flowchart of an image calibration method accordingto an embodiment of the present invention.

Referring to both FIG. 1 and FIG. 3, the first image capturing device120A and the second capturing device 120B capture a calibration objectfrom the first direction and the second direction so as to generate afirst calibration image and a second calibration image (Step S301). Tobe specific, the 3D data acquisition system 100 may perform acalibration parameter calculating process on the first image capturingdevice 120A and the second image capturing device 120B by using thecalibration object. In the present embodiment, the calibration objectmay be a board with a reference pattern. Such reference pattern may be acheck pattern. After the first image capturing device 120A and thesecond image capturing device 120B capture the calibration object, theymay respectively generate the first calibration image and the secondcalibration image.

Next, the image processing device 130 may process the first calibrationimage and the second calibration image so as to generate a firstintrinsic parameter, a first extrinsic parameter, and a first lensdistortion parameter corresponding to the first calibration image aswell as a second intrinsic parameter, a second extrinsic parameter, anda second lens distortion parameter corresponding to the secondcalibration image, where the first extrinsic parameter and the secondextrinsic parameter correspond to a same coordinate system (Step S303).The purpose of performing Step S303 is to obtain the parameters causingthe image distortions of the images captured by the first imagecapturing device 120A and the second image capturing device 120B.Herein, the first projection matrix is formed by the first intrinsicparameter and the first extrinsic parameter, and the second projectionmatrix is formed by the second intrinsic parameter and the secondextrinsic parameter.

To be specific, the first lens distortion parameter and the second lensdistortion parameter herein are the lens distortion coefficients of thefirst image capturing device 120A and the second image capturing device120B and usually represented by polynomials, which are used to describebarrel distortions or pincushion distortions caused by the lenses. Onthe other hand, intrinsic parameters may be used to describe thetransformation between camera coordinates and image coordinates. Thatis, the camera coordinates may be projected onto a projective planeaccording to the pinhole imaging principle, where the projective planeis normally written as a 3×3 matrix. The extrinsic parameters of thefirst image capturing device 120A and the second image capturing device120B are used to describe the transformation between the 3D worldcoordinates and the 3D camera coordinates and may be jointly written asa 3×4 composite matrix of a rotation matrix and a translation matrix.The first projection matrix and the second projection matrix may berepresented by Eq. (1.1) and Eq. (1.2) respectively:P=[p ₁ ^(T) ;p ₂ ^(T) ;p ₃ ^(T)]  Eq. (1.1)P=[p′ ₁ ^(T) ;p′ ₂ ^(T) ;p′ ₃ ^(T)]  Eq. (1.2)

Next, for each of the regions, the image processing device 130 mayperform an undistortion calculation on the first object image and thesecond object image respectively so as to generate a first correctedobject image and a second corrected object image (Step S305). In otherwords, after the image processing device 130 performs the undistortioncalculation on the first object image and the second object image byusing the first lens distortion parameter and the second lens distortionparameter, the first corrected object image and second corrected objectimage generated thereafter may be the corrected images approximate topinhole camera models.

FIG. 4 illustrates a flowchart of a 3D data acquisition method accordingto an embodiment of the present invention.

Referring to both FIG. 1 and FIG. 4, the light projecting device 110projects a laser light onto a plurality of regions of the surface of theobject A so as to generate a plurality of features within each of theregions (Step S401). For each of the regions, the first image capturingdevice 120A and the second image capturing device 120B capture theobject A and the features simultaneously and continuously from a firstdirection and a second direction respectively so as to generate aplurality sets of a first object image and a second object image (StepS403). That is, while the laser light projected by the light projectingdevice 110 is being swept through the surface of the object A, the firstimage capturing device 120A and the second image capturing device 120Bsimultaneously and continuously capture the object A and the features.The positions of the aforementioned regions may be decided by the user.The moving rate and the rotating pose of the light projecting device 110may affect the number of the first object images and the second objectimages. For example, for a fixed image capturing frequency of each ofthe first image capturing device 120A and the second image capturingdevice 120B, the faster the light projecting device 110 moves, the fewerthe first object images and the second object images are captured in thehorizontal direction by the first image capturing device 120A and thesecond image capturing device 120B; the fewer the rotating poses of theprojecting device 110, the fewer the first object images and the secondobject images are captured in the vertical direction by the first imagecapturing device 120A and the second image capturing device 120B.

Next, for each of the regions, the image processing device 130 performsan undistortion calculation on the first object image and the secondobject image so as to generate a first corrected object image and asecond corrected object image (Step S405) so that the first object imageand the second object image may be corrected to approximate to pinholecamera models. Step S405 may be referred to the related description inFIG. 3 and may not be repeated herein.

Next, the image processing device 130 obtains the 2D coordinates of aplurality of first features and a plurality of second featuresrespectively from the set of the first object image and the secondobject image corresponding to each of the regions (Step S407), where thefirst features are the features in the first corrected object images,and the second features are the features in the second corrected objectimages. The following description will be only focused on a single setof the first corrected object image and the second corrected objectimage.

FIG. 5A and FIG. 5B illustrate partially magnified images of the firstcorrected object image and the second corrected object image capturedsimultaneously. The image processing device 130 may filter the brightestpoints on each horizontal line in the first corrected object image andthe second corrected object image by setting a threshold. The values ofthe coordinates of the brightest points are integers in the y-direction(vertical direction) and floating numbers in the x-direction (horizontaldirection). The image processing device 130 may determine thecoordinates of the sub-pixels of the brightest points in the x-directionwith reference to the Gaussian distribution of the brightness values ofall the pixels. The hollow dots in FIG. 5A are the bright pointsfiltered from the first corrected object image; that is, theaforementioned first features. The hollow dots in FIG. 5B are the brightpoints filtered from the second corrected object image; that is, theaforementioned second features.

Revisiting FIG. 4, after Step S407, for each of the regions, the imageprocessing device 130 obtains the 2D coordinate of a correspondence ofeach of the first features from the second corrected object imageaccording to each of the first features and a first epipolar linecorresponding to each of the first features or obtains the 2D coordinateof a correspondence of each of the second features from the firstcorrected object image according to each of the second features and asecond epipolar line corresponding to each of the second features (StepS409). For each of the regions, the first feature point and itscorrespondence or the second feature point and its correspondence may bereferred to as “a corresponding set”.

To be specific, according to the computer vision theory, when a spatialpoint in the 3D space is captured by two cameras at different positionssimultaneously, the center of the two cameras, a corresponding setcaptured by the two cameras, and the aforementioned spatial point may bedescribed by epipolar geometry in the spatial domain. That is, thereexists a fundamental matrix representing such transformation. Byleveraging such concept, when there exists a feature X on the surface ofthe object A and when the feature X is captured by the first imagecapturing device 120A and the second image capturing device 120Bsimultaneously and calibrated by the image processing device 130, imagessuch as the first corrected object image in FIG. 5A and the secondcorrected object image in FIG. 5B may be generated. When the feature Xis projected onto the first corrected object image and forms a firstfeature x_(i), the plane formed by the joint line of the first featurex_(i) and the center of the first image capturing device 120A along withthe center of the first image capturing device 120B may intersect withthe second corrected object image.

Suppose that the first feature x_(i) in FIG. 5A may form an epipolarline l′_(i) in FIG. 5B through the fundamental matrix, where theepipolar line l′_(i) is the aforementioned first epipolar line. Theepipolar line l′_(i) and the joint line of a second feature x′_(k) andanother second feature x′_(k+1) may form an intersecting point x′_(i),where the point x′_(i) is the correspondence of the first feature x_(i).In other words, the first feature x_(i) and the point x′_(i) are theaforementioned corresponding set. It should be noted that, the distancefrom either the first feature x_(i) or the point x′_(i) to the epipolarline l′_(i) is less than a specific value such as 1.414 pixels;otherwise, the point x′_(i) may not be viewed as a valid correspondence.On the other hand, the correspondence of each of the second features inFIG. 5B may also be found in FIG. 5A via a second epipolar line (notshown).

After the image processing device 130 collects the two-coordinates ofall of the corresponding sets from the first corrected object image andthe second corrected object image of a same set, it may execute the sameprocess on the other sets of the first corrected object image and thesecond corrected object image. Next, the image processing device 130obtains the 3D data of the object A according to a first projectionmatrix, a second projection matrix, and the 2D coordinates of thecorresponding set corresponding to each of the regions (Step S411). Takethe feature X on the surface of the object A as an example. When thefeature X is projected onto the first corrected object image and forms afirst feature x, ideally, Eq. (2.1) may be satisfied:x×[PX]=0  Eq. (2.1)Similarly, in terms of a correspondence x′ of the first feature x in thesecond corrected object image, Eq. (2.2) may be satisfied:x′×[P′X]=0  Eq. (2.2)where P and P′ are the first projection matrix in Eq. (1.1) and thesecond projection matrix in Eq. (1.2) respectively. Moreover, the firstfeature x and the correspondence x′ of the first feature x may bewritten as Eq. (3.1) and Eq. (3.2) respectively:x=[x y 1]^(T)  Eq. (3.1)x′=[x′ y′ 1]^(T)  Eq. (3.2)Since the image processing device 130 has already obtained the firstprojection matrix P, the second projection matrix P′, and thecorresponding set x and x′ in the previous step, Eq. (4) may be furtherobtained therefrom:

$\begin{matrix}{{\begin{bmatrix}{{xp}_{3}^{T} - p_{1}^{T}} \\{{yp}_{3}^{T} - p_{2}^{T}} \\{{x^{\prime}p_{3}^{\prime\; T}} - p_{1}^{\prime\; T}} \\{{y^{\prime}p_{3}^{\prime\; T}} - p_{1}^{\prime\; T}}\end{bmatrix}X} = \begin{bmatrix}0 \\0 \\0 \\0\end{bmatrix}} & {{Eq}.\mspace{11mu}(4)}\end{matrix}$

Hence, the image processing device 130 may then obtain the 3D data ofthe feature X by singular value decomposition (SVD).

It should be noted that, since the laser light may generate a pluralityof features on the surface of the object A, and the 3D data of thefeatures may be calculated by the aforementioned algorithm, the user orthe moving mechanism may generate more features in the x-direction byrepeatedly sweeping the laser light so as to increase the scanresolution in the x-direction or generate more features in they-direction by slightly tilting the laser light so as to increase thescan resolution in the y-direction. Hence, the user or the movingmechanism may adjust the scan resolution of the light projecting device110 according to the surface complexity of an object. For example, theobject A includes a face region with a complex surface contour and abase region with a simple surface contour. If the light projectingdevice 110 scans the base region in a higher resolution, excessivefeatures may be generated. If the light projecting device 110 scans theface region in a lower resolution, the surface contour of the faceregion may not be completely modeled due to lack of samples.

Accordingly, after Step S411, the user or the moving mechanism maydetermine whether to finish acquiring the 3D data of the object A (StepS413). For example, the user may determine if the acquired 3D data ofthe object A is sufficient for constructing a 3D model of the object Aor not. When the user determines that the acquired 3D data of the objectA is insufficient, the 3D data acquisition system 100 may execute StepS401 so as to collect more 3D data of the object A.

When the user determines that the acquired 3D data of the object A issufficient, the 3D data acquisition system 100 may terminate the 3D dataacquisition process on the object A. Meanwhile, the image processingdevice 130 may generate a plurality of triangular meshes according tothe 3D data of the object A so as to accordingly construct the 3D modelof the object A (Step S415). Since there already exist a lot oftriangulation algorithms in the field of computer graphics, the detailsthereof may not be described herein.

To sum up, the method and the system for 3D data acquisition provided inthe present invention may generate a plurality of features on an objectthrough projecting a laser light onto a plurality of regions of theobject by the light projecting device. A plurality of image sets of theobject and the features may be captured by two image capturing devicesfrom different directions, and the 2D coordinates of the features in theimage sets may be calculated by an image processing device so as toobtain the 3D data of the object. Moreover, the moving rates, rotatingposes, and the number of repeating scans of the light projecting devicemay be adjusted according to the contour complexity of the object so asto adjust the scan resolutions in both the horizontal direction and thevertical direction. Such method and system of 3D data acquisition maynot only adjust the resolution with low costs, but may also processimages in real time so as to provide a higher applicability in practicaluse.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncover modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

What is claimed is:
 1. A three-dimensional data acquisition method,adapted to a three-dimensional data acquisition system having a lightprojecting device, two image capturing devices, and an image processingdevice for acquiring three-dimensional (3D) data of an object,comprising: projecting a linear laser light respectively onto aplurality of regions on a surface of the object by the light projectingdevice so as to form a plurality of features within each of the regions,wherein the regions comprise a first region and a second region withdifferent contour complexities, wherein moving rates, rotating poseswith respect to a horizontal direction and a vertical direction, and thenumbers of repeating scans that the linear laser light projects onto thefirst region and the second region are different, and each of theregions is a linear slit region or a curved slit region, and each of thefeatures are bright points; for each of the regions, capturing theobject and the features from a first direction and a second directionsimultaneously by the two image capturing devices respectively so as togenerate a first object image corresponding to the first direction andthe second object image corresponding to the second direction; for eachof the regions, processing the first object image and the second objectimage by the image processing device so as to obtain two-dimensional(2D) coordinates of the features in the first object image and thesecond object image comprising: performing an undistortion calculationon the first object image and the second object image by the imageprocessing device so as to generate a first corrected object image and asecond corrected object image wherein for each of the regions, the stepof performing the undistortion calculation on the first object image andthe second object image by the image processing device so as to generatethe first corrected object image and the second corrected object imagecomprises: performing the undistortion calculation on the first objectimage and the second object image by the image processing deviceaccording to the first lens distortion parameter and the second lensdistortion parameter so as to generate the first corrected object imageand the second corrected object image; obtaining 2D coordinates of aplurality of first features and a plurality of second features by theimage processing device, wherein the first features are the features inthe first corrected object image and the second features are thefeatures in the second corrected object image, wherein each of the firstfeatures and each of the second features are brightest points in eachhorizontal line, wherein values of the 2D coordinates of the firstfeatures and the second features are integers in the vertical direction,and wherein values of the 2D coordinates of the first features and thesecond features are floating numbers associated with sub-pixels in thehorizontal direction with reference to a Gaussian distribution ofbrightness values of all pixels in the first corrected object image andthe second corrected object image; and obtaining a 2D coordinate of acorrespondence of each of the first features from the second correctedobject image by the image processing device according to each of thefirst features and a first epipolar line corresponding to each of thefirst features as well as obtaining a 2D coordinate of a correspondenceof each of the second features from the first corrected object imageaccording to each of the second features and a second epipolar linecorresponding to each of the second features, wherein the correspondenceof each of the first features is an intersecting point between the firstepipolar line and a joint line of two of the second features, wherein adistance from each of the first features and a distance from thecorrespondence of each of the first features are less than a tolerancevalue; and wherein for each of the regions, before the step ofprocessing the first object image and the second object image by theimage processing device so as to obtain the 2D coordinates of thefeatures in the first object image and the second object image, themethod further comprises: capturing a calibration object from the firstdirection and the second direction respectively by the two imagecapturing devices so as to generate a first calibration imagecorresponding to the first direction and a second calibration imagecorresponding to the second direction; processing the first calibrationimage and the second calibration image by the image processing device soas to generate a first intrinsic parameter, a first extrinsic parameter,and a first lens distortion parameter corresponding to the firstcalibration image as well as a second intrinsic parameter, a secondextrinsic parameter, and a second lens distortion parametercorresponding to the second calibration image, wherein the firstextrinsic parameter and the second extrinsic parameter correspond to asame coordinate system; wherein the step of obtaining the 3D data of theobject by the image processing device according to the features in thefirst object image and the second object image corresponding to each ofthe regions comprises: obtaining the 3D data of the object by the imageprocessing device according to a first projection matrix, a secondprojection matrix, the 2D coordinates of the first featurescorresponding to each of the regions, the 2D coordinates of thecorrespondences of the first features corresponding to each of theregions, the 2D coordinates of the second features corresponding to eachof the regions, and the 2D coordinates of the correspondences of thesecond features corresponding to each of the regions, wherein the firstprojection matrix is a matrix formed by the first intrinsic parameterand the first extrinsic parameter, and wherein the second projectionmatrix is a matrix formed by the second intrinsic parameter and thesecond extrinsic parameter; and obtaining the 3D data of the object bythe image processing device according to the 2D data of the features inthe first object image and the second object image corresponding to eachof the regions.
 2. The 3D data acquisition method according to claim 1,wherein after the step of obtaining the 3D data of the object by theimage processing device according to the features in the first objectimage and the second object image corresponding to each of the regions,the method further comprises: generating a plurality of triangularmeshes by the image processing device according to the 3D data of theobject and accordingly constructing a 3D model of the object.
 3. Athree-dimensional (3D) data acquisition system, adapted to acquire 3Ddata of an object, comprising: a light projecting device, projecting alinear laser light respectively onto a plurality of regions on a surfaceof the object so as to form a plurality of features within each of theregions, wherein the regions comprise a first region and a second regionwith different contour complexities, and wherein moving rates, rotatingposes with respect to a horizontal direction and a vertical direction,and the numbers of repeating scans that the linear laser light projectsonto the first region and the second region are different, and each ofthe regions is a linear slit region or a curved slit region, and each ofthe features are bright points; a first image capturing device and asecond image capturing device, for each of the regions, capturing theobject and the features from a first direction and a second directionsimultaneously so as to generate a first object image corresponding tothe first direction and the second object image corresponding to thesecond direction; and an image processing device, for each of theregions, processing the first object image and the second object imageso as to obtain two-dimensional (2D) coordinates of the features in thefirst object image and the second object image, and obtaining the 3Ddata of the object according to the 2D data of the features in the firstobject image and the second object image corresponding to each of theregions, wherein the image processing device performs an undistortioncalculation on the first object image and the second object image by theimage processing device so as to generate a first corrected object imageand a second corrected object image, wherein the image processing deviceobtains 2D coordinates of a plurality of first features and a pluralityof second features by the image processing device, wherein the firstfeatures are the features in the First corrected object image and thesecond features are the features in the second corrected object image,wherein each of the first features and each of the second features arebrightest points in each horizontal line, wherein values of the 2Dcoordinates of the first features and the second features are integersin the vertical direction, and wherein values of the 2D coordinates ofthe first features and the second features are floating numbersassociated with sub-pixels in the horizontal direction with reference toa Gaussian distribution of brightness values of all pixels in the firstcorrected object image and the second corrected object image, andwherein the image processing device obtains a 2D coordinate of acorrespondence of each of the first features from the second correctedobject image by the image processing device according to each of thefirst features and a first epipolar line corresponding to each of thefirst features as well as obtaining a 2D coordinate of a correspondenceof each of the second features from the first corrected object imageaccording to each of the second features and a second epipolar linecorresponding to each of the second features; wherein the correspondenceof each of the first features is an intersecting point between the firstepipolar line and a joint line of two of the second features, wherein adistance from each of the first features and a distance from thecorrespondence of each of the first features are less than a tolerancevalue; and the first image capturing device and the second imagecapturing device further capture a calibration object from the firstdirection and the second direction so as to generate a first calibrationimage corresponding to the first direction and a second calibrationimage corresponding to the second direction, and the image processingdevice processes the first calibration image and the second calibrationimage so as to generate a first intrinsic parameter, a first extrinsicparameter, and a first lens distortion parameter corresponding to thefirst calibration image as well as a second intrinsic parameter, asecond extrinsic parameter, and a second lens distortion parametercorresponding to the second calibration image, wherein the firstextrinsic parameter and the second extrinsic parameter correspond to asame coordinate system.
 4. The 3D data acquisition system according toclaim 3, wherein for each of the regions, the image processing deviceperforms the undistortion calculation on the first object image and thesecond object image according to the first lens distortion parameter andthe second lens distortion parameter so as to generate the firstcorrected object image and the second corrected object image.
 5. The 3Ddata acquisition system according to claim 4, wherein the imageprocessing device obtains the 3D data of the object according to a firstprojection matrix, a second projection matrix, the 2D coordinates of thefirst features corresponding to each of the regions, the 2D coordinatesof the correspondences of the first features corresponding to each ofthe regions, the 2D coordinates of the second features corresponding toeach of the regions, and the 2D coordinates of the correspondences ofthe second features corresponding to each of the regions, wherein thefirst projection matrix is a matrix formed by the first intrinsicparameter and the first extrinsic parameter, and wherein the secondprojection matrix is a matrix formed by the second intrinsic parameterand the second extrinsic parameter.
 6. The 3D data acquisition systemaccording to claim 3, wherein the image processing device furthergenerates a plurality of triangular meshes according to the 3D data ofthe object and accordingly constructs a 3D model of the object.